The widow of Jimmy Mubenga, Makenda Kambana, right, at a demonstration. Mubenga died on a deportation flight to Angola after being 'heavily restrained' by a private security company. Photograph: Frank Baron for the Guardian

Police forces, prisons and youth detention centres face prosecution for corporate homicide from this week if an individual dies in their custody.

In the 10 years between 1999 and 2009, 333 people died in or following police custody, according to the Independent Police Complaints Commission. Ministry of Justice figures show that last year there were 58 self-inflicted deaths among prisoners in England and Wales.

Until now, the prison service, police forces and immigration units have not been subject to the new Corporate Manslaughter and Homicide Act, and there have been no successful prosecutions of police or prison officers, individually or at a senior management level, for institutional failures that have contributed to a death in custody.

But from 1 September a clause in the Corporate Homicide Act 2007 will come into place extending the law to cover all deaths in police custody suites, prison cells, mental health detention facilities, young offenders institutions and immigration suites. It will also cover Ministry of Defence institutions.

Prosecutions will take place if it can be proved that the way the facilities are managed or organised caused a death and amounted to a breach of the duty of care. The penalty for organisations convicted is a fine with no maximum limit. Crown Prosecution Service guidance says that the fines are likely to be in the many millions of pounds.

Deaths of people being transported to and from immigration detention centres – such as that of Jimmy Mubenga – will also be covered by the Corporate Homicide Act. But in the case of Mubenga, who died while being restrained on a British Airways plane to Angola last year, the private firm hired to transport him cannot be prosecuted under the Act because the law is not retrospective.

Campaigners for the families of those who die in custody believe the new law will provide extra protection for vulnerable individuals and at last inject some accountability into the system.

Helen Shaw, the co-director of Inquest, the charity that works with families of those who die in custody, said: "While not all deaths in custody are a result of grossly negligent management failings that would lead to consideration of a corporate manslaughter prosecution many of Inquest's cases have revealed a catalogue of failings in the treatment and care of vulnerable people in custody and raised issues of negligence, management failings and failures in the duty of care.

"The new provisions provide a new avenue to address these problems and will hopefully have a deterrent effect, preventing future deaths.

"We also welcome the government's decision to extend these corporate manslaughter provisions to the UK Border Agency … this is a positive step towards greater accountability."

Inquest said that until now, there had been no successful prosecutions for deaths in custody, even in the 10 cases since 1990 where an inquest jury had returned an unlawful killing verdict.

Implementation of the clause covering custody deaths was delayed in order to give police forces and prisons time to inspect their custody facilities and make sure they were up to the highest standards.

The Association of Chief Police Officers has been preparing for the implementation of the law. In 2008, Acpo issued new guidelines to all forces. But the Ministry of Justice has conceded that more work needs to be done to reduce the number of deaths in custody, specifically around improving healthcare, improving buildings and improving the level of staff training.

John Coppen, the Police Federation representative for custody sergeants, said: "This will mean the people at the top, who actually control the buildings and the budgets, have to think about their responsibilities. In future if someone was to hang themselves from a ligature in a cell, not only would the custody sergeant be questioned, but the authorities would look at the way the building was designed, whether there were any obvious ligature points that had not been removed, and the force could be held responsible."

As well as unlimited fines, courts can also impose an order requiring the company or organisation to publicise the fact that it has been convicted of the offence, and give details.